1. Field of the Invention
This invention relates to a flux cored wire electrode for self-shielded arc welding. More particularly, it relates to a flux cored wire electrode which is capable of providing weld metal having high toughness and free from welding defects such as pits and incomplete fusion, upon welding in any welding position.
2. Description of the Prior Art
Flux cored wire electrodes comprise a metal sheath filled with a flux. The main components of the flux generally used in said electrodes are CaF.sub.2, which serves as a slag-forming and shielding agent, Al, which serves as a deoxidizing and denitrifying agent, and Mg, which serves as a deoxidizing and shielding agent. The use of such flux cored wire electrodes makes it unnecessary to separately supply a shielding gas and a flux, hence is advantageous in that an improvement in welding efficiency is produced. Furthermore, such electrodes are excellent in weather resistance and have various other advantages.
At present, however, said wire electrodes are used only in specific instances of outdoor welding in civil engineering and construction and so on. Therefore, their advantages can hardly be said to be fully enjoyable. As the reasons for such limited use and delay in their coming into wide use in other fields, there may be mentioned the following disadvantages:
(1) Slag inclusion in the weld can easily take place, especially in multilayer welding. This is so in view that MgO and Al.sub.2 O.sub.3, both having a high melting point, are derived, for example, from Al, which is added as a deoxidizing and denitrifying agent, and Mg, which is added as a deoxidizing and shielding agent. Both MgO and Al.sub.2 O.sub.3 constitute the main components of the resulting slag.
(2) In addition to retention of a large amount of Al in the deposited metal, crystal grains tend to become coarser as a result of extraordinary decrease in oxygen (about 50-100 ppm), so that satisfactory notch toughness cannot be obtained.
(3) The resultant slag and molten metal assume an excessively high surface tension, so that bead dripping is apt to occur in the vertical-upward position or overhead position.
(4) The optimum arc voltage range is narrow, so that strict control of the voltage and/or electrode extension is required for the elimination of pits and blowholes.
(5) Since Mg and CaF.sub.2, which have high vapor pressure, are used in large amounts as flux constituents, a large amount of fume is generated and which contaminates the working environment to a considerable extent.